Fiberglass binders have a variety of uses ranging from stiffening applications where the binder is applied to woven or non-woven fiberglass sheet goods and cured, producing a stiffer product; thermo-forming applications wherein the binder resin is applied to sheet or lofty fibrous product following which it is dried and optionally B-staged to form an intermediate but yet curable product; and to fully cured systems such as building insulation.
Fibrous glass insulation products generally comprise matted glass fibers bonded together by a cured thermoset polymeric material. Molten streams of glass are drawn into fibers of random lengths and blown into a forming chamber where they are randomly deposited as a mat onto a traveling conveyor. The fibers, while in transit in the forming chamber and while still hot from the drawing operation, are sprayed with an aqueous binder. A phenol-formaldehyde binder is currently used throughout the fibrous glass insulation industry. The residual heat from the glass fibers and the flow of air through the fibrous mat during the forming operation are generally sufficient to volatilize the majority to all of the water from the binder, thereby leaving the remaining components of the binder on the fibers as a viscous or semi-viscous high solids liquid. The coated fibrous mat is transferred to a curing oven where heated air, for example, is blown through the mat to cure the binder and rigidly bond the glass fibers together.
Fiberglass binders used in the present sense should not be confused with matrix resins which are an entirely different and non-analogous field of art. While sometimes termed “binders”, matrix resins act to fill the entire interstitial space between fibers, resulting in a dense, fiber reinforced product where the matrix must translate the fiber strength properties to the composite, whereas “binder resins” as used herein are not space-filling, but rather coat only the fibers, and particularly the junctions of fibers. Fiberglass binders also cannot be equated with paper or wood product “binders” where the adhesive properties are tailored to the chemical nature of the cellulosic substrates. Many such resins, e.g. resorcinol/formaldehyde resins, are not suitable for use as fiberglass binders. One skilled in the art of fiberglass binders would not look to cellulosic binders to solve any of the known problems associated with fiberglass binders.
Binders useful in fiberglass insulation products generally require a low viscosity in the uncured state, yet characteristics so as to form a rigid thermoset polymeric mat for the glass fibers when cured. A low binder viscosity in the uncured state is required to allow the mat to be sized correctly. Also, viscous binders tend to be tacky or sticky and hence they lead to accumulation of fiber on the forming chamber walls. This accumulated fiber may later fall onto the mat causing dense areas and product problems. A binder which forms a rigid matrix when cured is required so that a finished fiberglass thermal insulation product, when compressed for packaging and shipping, will recover to its specified vertical dimension when installed in a building.
From among the many thermosetting polymers, numerous candidates for suitable thermosetting fiber-glass binder resins exist. However, binder-coated fiberglass products are often of the commodity type, and thus cost becomes a driving factor, generally ruling out such resins as thermosetting polyurethanes, epoxies, and others. Due to their excellent cost/performance ratio, the resins of choice in the past have been phenol/formaldehyde resins. Phenol/formaldehyde resins can be economically produced, and can be extended with urea prior to use as a binder in many applications. Such urea-extended phenol/formaldehyde binders have been the mainstay of the fiberglass insulation industry for years.
Over the past several decades, however, minimization of volatile organic compound emissions (VOCs) both on the part of the industry desiring to provide a cleaner environment, as well as by Federal regulation, has led to extensive investigations into not only reducing emissions from the current formaldehyde-based binders, but also into candidate replacement binders. For example, subtle changes in the ratios of phenol to formaldehyde in the preparation of the basic phenol/formaldehyde resole resins, changes in catalysts, and addition of different and multiple formaldehyde scavengers, has resulted in considerable improvement in emissions from phenol/formaldehyde binders as compared with the binders previously used. However, with increasing stringent Federal regulations, more and more attention has been paid to alternative binder systems which are free from formaldehyde.
One particularly useful formaldehyde-free binder system employs a binder comprising a polycarboxy polymer and a polyol. Formaldehyde-free resins are those which are not made with formaldehyde or formaldehyde-generating compounds. Formaldehyde-free resins do not emit appreciable levels of formaldehyde during the insulation manufacturing process and do not emit formaldehyde under normal service conditions. Use of this binder system in conjunction with a catalyst, such as an alkaline metal salt of a phosphorous-containing organic acid, results in glass fiber products that exhibit excellent recovery and rigidity properties.
While the binder compositions result in final products which have properties equal to or superior to those made with traditional binders, the compositions also present technical challenges. One such challenge is controlling the moisture of the product as it enters the curing oven. It has been found that if the residual moisture of the product entering into the curing oven exceeds 20 percent by weight of the product, uneven curing results which can detrimentally affect the performance of the product.
While it is possible to control the final moisture content of the uncured product by adjusting the amount of water introduced into the system. When the binder composition is formed, this system has been found to be inadequate. The system fails to take into account such factors as environmental humidity, temperature and the flow in the collection box, and the like. In addition, it has been found that the use of a high water content binder composition, improves the application of the binder to the fiber. Thus, it may, in fact, be desirable to start with a high water content binder composition yet have a perceived product with a relatively low moisture.
It is desirable to have a real time monitoring system that continuously monitors the moisture content of the pre-cured product. This information is then fed into a control system that is capable of adjusting one or more upstream variables to control the pre-cured product moisture.